1. Field of the Invention
The invention resides in the field of analytical spectrometers and more particularly relates to devices for preparing and manipulating samples for presentation to the optical component of the spectrometer.
2. Description of the Prior Art
Spectrometers and associated devices for the introduction and excitation of samples to be analyzed are well known in the prior art. One of the greatest areas of difficulty encountered in these instruments is the introduction of a representative sample into an excitation device such as a flame. In order to assure homogeniety of the sample to be analyzed, it is common practice to dissolve the sample, if not already in solution, and present the sample to the instrument in liquid form.
This practice, while dealing effectively with some of the problems of sample integrity, poses other problems in the excitation and analysis system. For example, the sample is usually nebulized and introduced into the excitation device as a mist of fine droplets. Pneumatic nebulizers are generally used and their efficiency is low, commonly 20 to 25%.
Further, the excitation process in prior art instruments includes desolvation, molecular dissociation, and atomic excitation all at one situs. As a result, a large fraction of the energy supplied to the excitation device is used in desolvation.
Additionally, the solvent is often a source of background interference in the measurement and the materials to be analyzed are present in a very dilute form, typically 1% sample in the final solution.
In spectrometers of more recent manufacture, non-flame excitation devices which operate through the dissipation of electrical energy have increasingly supplanted the use of traditional flame atomizers. These take the form of furnaces, rods, and filaments to which electrical power is applied to achieve the desired results.
In response to the problems described above, instruments have been devised which utilize graphite braid to support and supply energy to samples of minute quantity. These filaments have been heated to required temperatures by variable power sources employing electronic switching and feedback control to modulate the power supplied to the braid.
In contrast, the invention disclosed herein presents a system which connects a filament successively to a plurality of contact points, each supplying a level of power to accomplish a particular purpose such as desolvation, ashing, and excitation. By utilizing separate contacts, either the filament or the contacts may be moved to effect a change in power allowing a number of filaments to undergo heating simultaneously. Thus one filament and sample may successively be carried through preparatory and excitation steps while others are subjected to similar treatment in a progressive manner. In this way, an automatic cycle may be established to allow the analysis of samples on a periodic and regular basis yielding a continuous determination of the content of the material from which the sample is drawn.
This feature is particularly useful in the analysis of waste effluents, gases and liquids, which are the products of continuous industrial operations.
Other features and advantages of the invention will become more clear from the summary and description of the preferred embodiment which follow.